1. Field of the Invention
The present invention relates to a method of driving a fluid by transmitting ultrasound in the fluid, and more particularly to a fluid drive method which facilitates the control of a driving force generated by ultrasound.
2. Description of the Prior Art
There is a phenomenon known as acoustic streaming, which refers to flow currents set up in a fluid that is generated with powerful ultrasonic waves. While former research into acoustic streaming has used continuous ultrasonic waves, recently the use of pulsed ultrasound to set up flow currents in a fluid has been reported (Ultrasound in Med. & Biol. Vol. 15, No. 4, pp. 363-373, 1989).
A possible application for acoustic streaming is to utilize it in devices that generate fluid flows, such as pumps and stirrers. For such an application, given the same driving force to the fluid, the smaller the ultrasonic energy the better, as it enables the apparatus to be made smaller and reduces energy costs. Moreover, the ability to control the generated flow current by controlling the driving force makes it possible to generate a flow in a limited region and, therefore, broadens the range of possible applications.
The object of the present invention is therefore to provide a method of driving a fluid by using ultrasonic waves wherein the intensity of the force used to drive the fluid can be readily controlled through ultrasound and the distribution of the fluid driving force can be adjusted.